Fourier Transform (FT) mass analyzers are widely used in the mass spectrometry field for acquisition of high-resolution, accurate mass (HRAM) data. Examples of commercially-available FT mass analyzers include the orbital electrostatic trap mass analyzer (a version of which is sold as the Orbitrap mass analyzer by Thermo Fisher Scientific) and the ion cyclotron resonance (ICR) mass analyzer. Generally described, FT mass analyzers utilize electric or electromagnetic fields to confine ions to a trapping region, where the ions undergo periodic motion having frequencies characteristic of their mass-to-charge ratios (m/z's). A detector is utilized to measure a time-varying signal, referred to as a transient, generated by the motion of the trapped ions, and the transient is subsequently processed by performing a Fourier transform to convert it to the frequency space and thereby identify the characteristic frequencies representative of the ions' m/z's.
It is known that the performance of FT mass analyzers may be adversely affected by the interaction of ions with similar characteristic frequencies (see, e.g., Grinfield et al., “Crowd Control of Ions in Orbitrap Mass Spectrometry”, 60th Amer. Soc. Mass Spectr. Conference Proceedings, 2012). Under certain operating conditions, the interaction of two adjacent ions (ions of closely spaced mass-to-charge ratios (m/z's)) results in a shift of both of their frequencies towards the other. This phenomenon may result in the coalescence (i.e., merging) of two closely spaced peaks in the mass spectrum into a single unresolved peak. Such a result is particularly problematic when it is desirable to separately identify or quantify closely spaced ions, for example ions of isotopologue species having identical molecular compositions but with different isotopic substitutions.